opengl - Clipping a sphere -


had asked question here: drawing portion of hemisphere airspace

probably more gis have moved more basic , specific implementation in opengl desired output.

i have overridden/copied functions drawing hemisphere , altering gl part insert clipping. able draw hemisphere centred @ location (latitude,longitude) , radius may 2000. when cut using plane nothing happens. please check equation of plane(its plane parallel surface of globe @ height may 1000, (0,0,+1,1000))

the base class has drawunitsphere might causing problems trying use gl's glusphere(). can't see sphere on globe. used translate shift location(lat/lon) still can't see it. might issues lat/lon , cartesian coordinates, or placing of clipping code. please check.

here code:

@override public void drawsphere(drawcontext dc) {     double[] altitudes = this.getaltitudes(dc.getverticalexaggeration());     boolean[] terrainconformant = this.isterrainconforming();     int subdivisions = this.getsubdivisions();      if (this.isenablelevelofdetail())     {         detaillevel level = this.computedetaillevel(dc);          object o = level.getvalue(subdivisions);         if (o != null && o instanceof integer)             subdivisions = (integer) o;                 }      vec4 centerpoint = this.computepointfromposition(dc,         this.location.getlatitude(), this.location.getlongitude(), altitudes[0], terrainconformant[0]);      matrix modelview = dc.getview().getmodelviewmatrix();     modelview = modelview.multiply(matrix.fromtranslation(centerpoint));     modelview = modelview.multiply(matrix.fromscale(this.getradius()));     double[] matrixarray = new double[16];     modelview.toarray(matrixarray, 0, false);      this.setexpirytime(-1l); // sphere geometry never expires.      gl gl = dc.getgl(); // gl initialization checks gl2 compatibility.     gl.glpushattrib(gl.gl_polygon_bit | gl.gl_transform_bit);     try     {          gl.glenable(gl.gl_cull_face);         gl.glfrontface(gl.gl_ccw);          // applying scale transform on modelview matrix, normal vectors must re-normalized         // before lighting computed. in case we're scaling constant factor, gl_rescale_normal         // sufficient , potentially less expensive gl_normalize (or computing unique normal vectors         // each value of radius). gl_rescale_normal introduced in opengl version 1.2.         gl.glenable(gl.gl_rescale_normal);          gl.glmatrixmode(gl.gl_modelview);         gl.glpushmatrix();          //clipping         doublebuffer eqn1 = bufferutils.createdoublebuffer(8).put(new double[] {0, 0, 1, 100});         eqn1.flip();         gl.glclipplane(gl.gl_clip_plane0, eqn1);         gl.glenable(gl.gl_clip_plane0);         try         {             gl.glloadmatrixd(matrixarray, 0);             //this.drawunitsphere(dc, subdivisions);             gl.glloadidentity();             gl.gltranslatef(75.2f, 32.5f, 0.0f);             gl.glcolor3f(1.0f, 0.0f, 0.0f);             glu glu = dc.getglu();             gluquadric qd=glu.glunewquadric();             glu.glusphere(qd,3.0f,20,20);         }                 {             gl.glpopmatrix();         }     }         {         gl.glpopattrib();     } }  @override public void drawunitsphere(drawcontext dc, int subdivisions) {     object cachekey = new geometry.cachekey(this.getclass(), "sphere", subdivisions);     geometry geom = (geometry) this.getgeometrycache().getobject(cachekey);     if (geom == null || this.isexpired(dc, geom))     {         if (geom == null)             geom = new geometry();         this.makesphere(1.0, subdivisions, geom);         this.updateexpirycriteria(dc, geom);         this.getgeometrycache().add(cachekey, geom);     }      this.getrenderer().drawgeometry(dc, geom); }  @override public void makesphere(double radius, int subdivisions, geometry dest) {     geometrybuilder gb = this.getgeometrybuilder();     gb.setorientation(geometrybuilder.outside);      geometrybuilder.indexedtrianglearray ita = gb.tessellatesphere((float) radius, subdivisions);     float[] normalarray = new float[3 * ita.getvertexcount()];     gb.makeindexedtrianglearraynormals(ita, normalarray);      dest.setelementdata(gl.gl_triangles, ita.getindexcount(), ita.getindices());     dest.setvertexdata(ita.getvertexcount(), ita.getvertices());     dest.setnormaldata(ita.getvertexcount(), normalarray); }


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